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North
Cascades National Park |
Site Name
IMPROVE:
NOCA1
CASTNET: NCS415
Region
Cascade Range
Terrain
Terrain is shown in the 2 km terrain map and the 20 km terrain map.
North Cascades National Park occupies
684,000 acres in the western slopes of the Cascade Range of northern
Washington, adjacent to the Canadian border. It consists of a north and a
south section, separated by the Skagit River that flows westward from the
Cascade Crest just east of the National Park into northern Puget Sound 60 to
70 km (40 mi) west of the National Park boundary. The Park’s primary
drainage is the Skagit River and tributaries, which link it to the northern
Puget Sound area. Lowest Park elevations are near 200 to 300 m (~ 700 ft or
higher) at locations in the Skagit River valley between the two Park
sections. Highest summit elevations are 2,750 to 2,775 m (9,000 to 9,100 ft)
The IMPROVE site representing North Cascades National Park is NOCA1, near
Ross Lake on the upper reaches of the Skagit River just outside of the
eastern boundary of the northern Park section, elevation 576 m (1,889 ft),
87 m (285 ft) above lake level. The
North Cascades CASTNET site, NCS415, is also located in the Skagit River
valley 34 km (21 mi) downstream from NOCA1, at an elevation of 109 m (358
ft), 467 m (1,532 ft) lower than the NOCA1 elevation.
Representativeness
The NOCA1 IMPROVE site is at lower elevation of the Skagit River valley near
Ross Lake, 87 m above lake level and about 200 m below the surrounding ridge
tops. It should be representative of lower Park elevations at all times. It
may at times be contained within surface based valley inversions that do not
extend to higher Park elevations.
Nearby Population/Industrial Centers
The northern Puget Sound area near the mouth of the Skagit River is ~ 100 km
(60 mi) west of the NOCA1. The city of Seattle is 160 km (100 mi) southwest.
Nearby Meteorological Network Monitoring Sites
Nearby meteorological monitoring network stations are shown in the data
network map and at the
RAWS station US Climate Archive
site. The North Cascades NP CASTNET
site, NCS415, is probably the best source for hourly meteorological data,
including wind data, representative of concurrent meteorological conditions
at NOCA1. The nearest upper air site is at Quillayute Washington (UIL), on
the Olympic Peninsula. This and other upper air sites are accessible via the
University of Wyoming Dept
of Atmospheric Science web page.
Wind Patterns
Synoptic winds in the region are generally westerly, with more northwesterly
flow during the summer when the Pacific High is off the coast of
northwestern U.S., and more westerly flow during the winter when the Pacific
High has retreated southward. This pattern can be seen in monthly
Seattle Washington wind
roses although these surface wind patterns may differ somewhat from
upper level winds because of terrain effects. During the winter, with high
pressure over the Great Basin and Idaho and low pressure west of the
Cascades easterly gradient (synoptic) flow is common.
The NOCA1 IMPROVE site is within the upper Skagit River channeled flow
regime, with westerly channeled upvalley flow enhanced at times by
prevailing westerly synoptic flow. Correlation with hourly wind direction
data from the CASTNET NCS415 site may reveal low level transport from the
Puget Sound source region. If it occurs, such transport would likely be
indicated by a diurnal pattern to monitored aerosol concentrations.
Inversions/Trapping
Locally, the NOCA1 site is in a lower valley location and may at times be
within valley trapping inversions that do not extend to higher National Park
elevations. On a larger scale, inversion breakup and vertical mixing during
periods of weak synoptic forcing could at times bring urban emissions from
Seattle and northern Puget Sound 100 to 160 km to the west into the area.
Mixing heights calculated for Salem Oregon (Ferguson
and Rorig, 2003), a maritime location similar to the Seattle and Puget
sound region, show winter heights generally below 300 m (1,000 ft), which
would prevent urban emissions from reaching the NOCA1 site elevation, but
Spring and summer Salem mixing heights frequently reach to 1,500 m or higher
which could allow Puget Sound urban emissions to mix to the NOCA1 elevation.
Resulting transport to NOCA1 could result from concurrent afternoon upvalley
flow or from entrainment of emissions near the mixing height into higher
level air flow, and subsequent transport to the monitoring site. Calculated
Fall Salem mixing heights were typically 300 to 600 m, lower than in the
spring and summer but occasionally high enough to bring valley emissions to
the NOCA1 site elevation.
Regionally, summertime subsidence inversions associated with the
establishment of the semi-permanent Pacific high-pressure system could
result in regional aerosol buildup over periods of days. Subsidence
inversion heights are typically at elevations of 2,000 to 3,000 m (6,000 to
10,000 ft), well above the NOCA1 IMPROVE site. With weak northwesterly
winds, Puget Sound emissions can become trapped against the Cascades and/or
pushed up the Skagit River valley towards the NOCA1 IMPROVE site. Highest
regional aerosol concentrations may occur during summertime stagnation and
subsidence inversion periods in conjunction with western wildland fires.
Climatological Statistics
Seattle
Washington Normals Means and Extremes are representative of low
elevation locations in western Washington source areas upwind of North
Cascades National Park. Other
Washington Climate
Summaries are available from the
Western Regional Climate Center.
Meteorological Indicators
Keywords (to be completed)
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Last updated 28 February 2005
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